Anionic polymerization of a lactam such as a caprolactam in the presence of an anionic polymerization catalyst and a polymerization activator is a well known technique, and the method is known in which by using this process, polymerization is conducted in-situ in molding to produce various kinds of molded articles including large molding products.
Polyamides, such as a polycaprolactam, obtained by anionic polymerization have the advantage that they have a high crystallinity and are excellent in properties such as mechanical strength, wear resistance, creep resistance and chemical resistance. On the other hand, however, those polyamides are known to have the disadvantage that they are low in resistance to impact, poor in breaking elongation and lack in toughness. As technical means to overcome the disadvantage, the use of a substituted amide monomer, such as N,N-dimethylbenzamide, N,N-dimethylacetamide and N-methylpyrrolidone, as a plasticizer has been proposed. For example, Patent Document 1 discloses the use of an N-alkyl pyrrolidone having a lower alkyl substituent, and describes that the alkyl group has 1 to 4 carbon atoms, and is most preferably methyl or ethyl. However, since the monomeric plasticizer tends to bleed out, its effect is lost over time. Therefore, the use of a polymeric plasticizer has been proposed. For example, Patent Document 2 discloses anionic polymerization conducted in the presence of nylon 11. In Patent Document 3, a highly branched aromatic compound-based polymer is used, and the polymer is bound to a polyamide.
Also, a method of modifying a polyamide by forming the polyamide into a block copolymer has been contemplated. For example, Patent Document 4 and documents cited therein, Patent Document 5 and Patent Document 6 disclose modifying a polyamide by forming the polyamide into a block copolymer, and Patent Document 7 discloses a modification method of conducting polymerization in the presence of a prepolymer of carbamoyl lactam and polyol.
However, the conventional production processes are unfavorable to polymerization in-situ in a molding stage because there is the disadvantage that the polymerization time is increased due to addition of other polymers to a polymerization system, and also the viscosity of a raw material is caused to rise, and additional steps are required in production of a polyamide. Further, the disadvantage can be pointed out that impact strength is not necessarily sufficiently improved.